Being Popular

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| May 2001(This article was written as a kind of business plan for a
new language.
So it is missing (because it takes for granted) the most important
feature of a good programming language: very powerful abstractions.)A friend of mine once told an eminent operating systems
expert that he wanted to design a really good
programming language. The expert told him that it would be a
waste of time, that programming languages don't become popular
or unpopular based on their merits, and so no matter how
good his language was, no one would use it. At least, that
was what had happened to the language he had designed.What does make a language popular? Do popular
languages deserve their popularity? Is it worth trying to
define a good programming language? How would you do it?I think the answers to these questions can be found by looking
at hackers, and learning what they want. Programming
languages are for hackers, and a programming language
is good as a programming language (rather than, say, an
exercise in denotational semantics or compiler design)
if and only if hackers like it.1 The Mechanics of PopularityIt's true, certainly, that most people don't choose programming
languages simply based on their merits. Most programmers are told
what language to use by someone else. And yet I think the effect
of such external factors on the popularity of programming languages
is not as great as it's sometimes thought to be. I think a bigger
problem is that a hacker's idea of a good programming language is
not the same as most language designers'.Between the two, the hacker's opinion is the one that matters.
Programming languages are not theorems. They're tools, designed
for people, and they have to be designed to suit human strengths
and weaknesses as much as shoes have to be designed for human feet.
If a shoe pinches when you put it on, it's a bad shoe, however
elegant it may be as a piece of sculpture.It may be that the majority of programmers can't tell a good language
from a bad one. But that's no different with any other tool. It
doesn't mean that it's a waste of time to try designing a good
language. Expert hackers
can tell a good language when they see
one, and they'll use it. Expert hackers are a tiny minority,
admittedly, but that tiny minority write all the good software,
and their influence is such that the rest of the programmers will
tend to use whatever language they use. Often, indeed, it is not
merely influence but command: often the expert hackers are the very
people who, as their bosses or faculty advisors, tell the other
programmers what language to use.The opinion of expert hackers is not the only force that determines
the relative popularity of programming languages — legacy software
(Cobol) and hype (Ada, Java) also play a role — but I think it is
the most powerful force over the long term. Given an initial critical
mass and enough time, a programming language probably becomes about
as popular as it deserves to be. And popularity further separates
good languages from bad ones, because feedback from real live users
always leads to improvements. Look at how much any popular language
has changed during its life. Perl and Fortran are extreme cases,
but even Lisp has changed a lot. Lisp 1.5 didn't have macros, for
example; these evolved later, after hackers at MIT had spent a
couple years using Lisp to write real programs. [1]So whether or not a language has to be good to be popular, I think
a language has to be popular to be good. And it has to stay popular
to stay good. The state of the art in programming languages doesn't
stand still. And yet the Lisps we have today are still pretty much
what they had at MIT in the mid-1980s, because that's the last time
Lisp had a sufficiently large and demanding user base.Of course, hackers have to know about a language before they can
use it. How are they to hear? From other hackers. But there has to
be some initial group of hackers using the language for others even
to hear about it. I wonder how large this group has to be; how many
users make a critical mass? Off the top of my head, I'd say twenty.
If a language had twenty separate users, meaning twenty users who
decided on their own to use it, I'd consider it to be real.Getting there can't be easy. I would not be surprised if it is
harder to get from zero to twenty than from twenty to a thousand.
The best way to get those initial twenty users is probably to use
a trojan horse: to give people an application they want, which
happens to be written in the new language.2 External FactorsLet's start by acknowledging one external factor that does affect
the popularity of a programming language. To become popular, a
programming language has to be the scripting language of a popular
system. Fortran and Cobol were the scripting languages of early
IBM mainframes. C was the scripting language of Unix, and so, later,
was Perl. Tcl is the scripting language of Tk. Java and Javascript
are intended to be the scripting languages of web browsers.Lisp is not a massively popular language because it is not the
scripting language of a massively popular system. What popularity
it retains dates back to the 1960s and 1970s, when it was the
scripting language of MIT. A lot of the great programmers of the
day were associated with MIT at some point. And in the early 1970s,
before C, MIT's dialect of Lisp, called MacLisp, was one of the
only programming languages a serious hacker would want to use.Today Lisp is the scripting language of two moderately popular
systems, Emacs and Autocad, and for that reason I suspect that most
of the Lisp programming done today is done in Emacs Lisp or AutoLisp.Programming languages don't exist in isolation. To hack is a
transitive verb — hackers are usually hacking something — and in
practice languages are judged relative to whatever they're used to
hack. So if you want to design a popular language, you either have
to supply more than a language, or you have to design your language
to replace the scripting language of some existing system.Common Lisp is unpopular partly because it's an orphan. It did
originally come with a system to hack: the Lisp Machine. But Lisp
Machines (along with parallel computers) were steamrollered by the
increasing power of general purpose processors in the 1980s. Common
Lisp might have remained popular if it had been a good scripting
language for Unix. It is, alas, an atrociously bad one.One way to describe this situation is to say that a language isn't
judged on its own merits. Another view is that a programming language
really isn't a programming language unless it's also the scripting
language of something. This only seems unfair if it comes as a
surprise. I think it's no more unfair than expecting a programming
language to have, say, an implementation. It's just part of what
a programming language is.A programming language does need a good implementation, of course,
and this must be free. Companies will pay for software, but individual
hackers won't, and it's the hackers you need to attract.A language also needs to have a book about it. The book should be
thin, well-written, and full of good examples. K&R is the ideal
here. At the moment I'd almost say that a language has to have a
book published by O'Reilly. That's becoming the test of mattering
to hackers.There should be online documentation as well. In fact, the book
can start as online documentation. But I don't think that physical
books are outmoded yet. Their format is convenient, and the de
facto censorship imposed by publishers is a useful if imperfect
filter. Bookstores are one of the most important places for learning
about new languages.3 BrevityGiven that you can supply the three things any language needs — a
free implementation, a book, and something to hack — how do you

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